Use of cross-protection to identify novel vaccine candidates for infectious agents

Abstract

This invention discloses methods for identifying Francisella tularensis vaccine candidates. It enables identification of novel vaccine candidates and quality assurance for vaccine batches, assessment of protection in vaccinates and identification of the infecting agent in vaccinates. Mice were first vaccinated with Brucella abortus O-polysaccharide (OPS) vaccine. These animals were then given 10 LD 50 s of F. tularensis live vaccine strain (LVS). Sixty percent (60%) of the vaccinated mice survived the multiple lethal doses. Sera were collected from these surviving mice and the antibodies were used to probe supernatant and cell lysates of live F. tularensis LVS cultures. Several F. tularensis components were identified only by the noted “survivor” antisera. Of these identified proteins, enzyme digestions and chemical oxidation suggest post-translational modifications of some proteins e.g. a 52 kDa glycoprotein, a 45 kDa lipoprotein and a 19 kDa nucleoprotein. The 52 kDa component caused nitrous oxide induction in tissue cultures at low concentrations, cell death at high concentrations. Vaccination with this gave partial protection while addition of other components acted synergistically to give enhanced protection from 250 LD 50 s of F. tularensis LVS.

1. An isolated subcellular protein having a molecular weight of about 52 kDa, said protein having been expressed from a  Francisella tularensis  subculture growing in synthetic salts medium at pH 6.5. 
     
     
       2. The subcellular protein of  claim 1 , wherein said protein is identified by immunological reaction with an antiserum or antibodies from said antiserum, said antiserum having been obtained from an animal which has been first vaccinated with O-polvsaccharide extracted from a  B. abortus , which is immunologically cross-reactive with  Francisella tularensis , and then survived challenge with a dose of the  Francisella tularensis  which would be lethal in the absence of said first vaccination.